Defective LPS signaling in C3H/HeJ and C57BL/10ScCr mice: mutations in Tlr4 gene.

Mutations of the gene Lps selectively impede lipopolysaccharide (LPS) signal transduction in C3H/HeJ and C57BL/10ScCr mice, rendering them resistant to endotoxin yet highly susceptible to Gram-negative infection. The codominant Lpsd allele of C3H/HeJ mice was shown to correspond to a missense mutation in the third exon of the Toll-like receptor-4 gene (Tlr4), predicted to replace proline with histidine at position 712 of the polypeptide chain. C57BL/10ScCr mice are homozygous for a null mutation of Tlr4. Thus, the mammalian Tlr4 protein has been adapted primarily to subserve the recognition of LPS and presumably transduces the LPS signal across the plasma membrane. Destructive mutations of Tlr4 predispose to the development of Gram-negative sepsis, leaving most aspects of immune function intact.

The central nervous system in childhood leukemia. III. Mineralizing microangiopathy and dystrophic calcification.

We determined the prevalence, histopathologic features, and clinical correlations of a distinctive vascular lesion within the central nervous system (CNS) of children who died with acute lymphoblastic leukemia (ALL). Of 163 brains examined at autopsy, 28 (17%) had a noninflammatory mineralizing microangiopathy, usually accompanied by varying amounts of necrosis and calcification in adjacent neural tissue. The lesion always involved the lenticular nucleus with or without additional involvement of cerebral cortex. It was not the cause of death in any patient. An analysis of clinical features common to patients with microangiopathy indicated that cranial irradiation, in doses as low as 1500 rad, had induced the degenerative process. Survival beyond 10 months from the time of irradiation and multiple postirradiation CNS leukemic relapses, both had significant influences on the development of the lesion. Chemotherapy, particularly systemic or intrathecal methotrexate, might have contributed to the disease process, but apparently was not the instigating factor. Patients at greatest risk for developing microangiopathy are those under 10 years of age at the time of cranial irradiation, who then live more than 10 months and develop multiple CNS leukemic relapses.

Genetic and physical mapping of the Lps locus: identification of the toll-4 receptor as a candidate gene in the critical region.

On the basis of 2093 meioses analyzed in two separate intraspecific backcrosses, the location of the mouse Lpsd mutation was circumscribed to a genetic interval 0.9 cM in size. A total of 19 genetic markers that lie in close proximity to the mutation were examined in mapping. Most of these were previously unpublished polymorphic microsatellites, identified by fragmentation of YAC and BAC clones spanning the region of interest. Lpsd was found to be inseparable from the microsatellite marker D4MIT178, and from three novel polymorphic microsatellites identified near D4MIT178. The mutation was confined between two novel microsatellite markers, herein designated "B" and "83.3." B lies centromeric to the mutation, and was separated by four crossovers in a panel of 1600 mice; 83.3 lies distal to the mutation and was separated by three crossovers in a panel of 493 mice. 66 BAC clones and one YAC clone were assembled to cover > 95% of the critical region. Estimates based on pulsed field gel electrophoresis and fluorescence in situ hybridization indicate that the The B-->83.3 interval is about 3.2 Mb in length. A minimal area of zero recombinational distance from Lpsd was also assigned, and found to occupy approximately 1.2 Mb of physical size. To identify gene candidates, nearly 40,000 sequencing runs were performed across the critical region. Selective hybridization and exon trapping were also employed to identify genes throughout the "zero" region. Only a single intact gene was identified within the entire critical region. This gene encodes the Toll-4 receptor, a member of the IL-1 receptor family.